1. Field of Invention
This invention relates to a lamp burnout detecting unit which detects the burnout of a lamp, such as a tail lamp or a stop lamp of an automobile.
2. Description of Related Art
Conventionally, the stop lamp or tail lamp of an automobile, which is connected through a switch or similar device to the battery, is provided with a device for detecting the burnout of the stop lamp or tail lamp.
FIG. 4 is a wiring diagram showing a battery and rear combination lamps with a lamp burnout detecting unit (hereinafter "a burnout detecting unit"). The power of the battery 120, which is disposed in the front of a vehicle 100, is supplied to the rear of the vehicle 100 through a tail switch 121 and a stop switch 122. The power is supplied to the rear of the vehicle 100 via a floor harness 123, which is connected to a joint connector 124 in the rear of the vehicle, so that the power of the battery 120 is supplied through the joint connector 124 to the burnout detecting unit 111 and the rear combination lamps 130 and 140.
Specifically, when the tail switch 121 and the stop switch 122 are in an "on" position (turned on), the wires of the floor harness 123, which are connected to a +B wire (connected to the positive (+) terminal) of the battery 120, are connected to the burnout detecting unit 111. The wire extending from the tail switch 121 is connected to first terminals of tail lamps 131 and 141. The wire extending from the stop switch 122 is connected to first terminals of stop lamps 132 and 142. The remaining second terminals of the lamps of the rear combination lamps 130 and 140 are connected through a rear harness to the joint connector 124, and grounded through the floor harness.
As is apparent from the above description, when the tail switch 121 or the stop switch 122 is turned on and off, the corresponding lamp is turned on and off. The burnout detecting unit 111 monitors current flowing to the lamps, so as to detect the burnout of a lamp or lamps from a decrease in the current value.
The conventional burnout detecting unit is subject to the problem that its wiring is rather intricate.
FIG. 5 is a wiring diagram showing a battery, rear combination lamps and other lamps with a conventional burnout detecting unit. In the floor harness 123, the wire (TAIL) that extends from the tail switch 121, as shown in FIG. 4, is connected to first terminals of right and left license plate lamps 151 and 152 and to a burnout detecting unit 111 through joint connector 124. The wire connected to the burnout detecting unit 111 is connected to first terminals of tail lamps 131a, 131b, 141a and 141b through joint connector 124b.
In the floor harness 123, the wire (STOP) that extends from the stop switch 122, as shown in FIG. 4, is connected through the burnout detecting unit 111 to a first terminal of a high mount stop switch 155, and through joint connector 124b to first terminals of stop lamps 132a, 132b, 142a and 142b.
Furthermore, the floor harness 123 includes +B wires connected through joint connector 124c to right and left backup (B/U lamps 153 and 154.
With respect to the +B wires, the ground (GND) wire of the floor harness 123 is connected through joint connector 124a to the grounded side (not shown) of the burnout detecting unit 111 and to the remaining second terminals of the right and left combination lamps 130 and 140, the right and left license plate lamps 151 and 152, the right and left backup lamps 153 and 154, and the high mount stop lamp 155.
As is apparent from the above description, in the wiring of the conventional burnout detecting unit 111, a plurality of +B wires and the ground wire of the floor harness are distributed to the respective lamps through a plurality of joint connectors. Therefore, the resultant wiring is unavoidably intricate; that is, it is rather difficult to provide the wiring of the lamps. Hence, it is also difficult to automatically lay wires for the lamps. The use of the joint connectors results in an increase in manufacturing costs. The joint connectors also require spaces for their installation.